help my truck keeps killing the battery

[mikev]

Ok guys its a 2000 GMC yukon xl with a 5.3 v8. It started about a week ago something is draining the battery and i end up having to jump it off and put the charger on it when i get home. so far i have had the battery and alternator tested twice both are good alternator putting out 106 amps. I cleaned and checked all the connections this didnt help. I sat and pulled all the fuses one by one with the ignition on to see what was causing such a big draw and killing the battery but nothing changed the ammount of amps it was drawing when i did this. I am thinking there is a short in the starter maybe? would they be able to test for that at the auto parts store if i pull the starter or do you guys have any other ideas.

[MOP]

There is so much electrical junk on the new vehicles that can and does go wrong, I had a similar problem on my GMC sub which turned out to be a light module. I would come home get out and lock the truck, the automatic interior lights would stay lit for a few seconds and go out as usual. What would happen after 10-15 minutes is the interior lights would come on and stay on draining the battery. You probably need a trip to a dealer.

Phil

[Formula Jr]

Phil is right, there's just too many places to look for this drain in a modern car that leaves stuff on once you think you've turned it off. And as you said you unpluged all the fuses to see if that would help and it didn't. The battery charges up on the alt. But does the Alt stop feeding off the battery to make a magnetic field? Voltage regulator with a welded relay? Thats the only thing I can think of that would run a battery down over night with out being an obvious a load like a light or something.

[mikev]

it doesnt run it down over night it will sit fine for days. It runs it down when the truck is running thats why my inital thought was the alternator but testing shows it good. thats why i am thinking a starter because as soon as you turn the key on it starts sucking the amps and pulling fuses doesnt drop it. guess i may have to take it to the dealer bummer.

[Formula Jr]

A Theory.

Bench testing the alt will just tell you that the alt works and that the diodes are good. But while in the truck, and running the alt isn't getting energized from the battery. Its a total loss ignition system at that point and purely running off the battery to fire the plugs. So the voltage regulator isn't supplying power from the battery to the stator of the alternator to create the field in which the rotator spins under engine power to make more electricity. Its a feed back loop controlled by the voltage regulator. You can test this very easily.
a Battery has a resting voltage. Take a VOM meter and take a DC Volt reading across the + and - terminals. Then start the truck. You should see 14.7 Volts or so, ie the reading should increase to 14.7. If the reading doesn't change to higher value or went lower in voltage then there is something wrong with the charging circuit and the regulator.

The starter motor would not have been my first place to look. They just sit there grounded to the motor, with the motor strapped to the ground terminal of the Bat. It only receives power from the battery once the key switch goes to start and that sends out the solenoid relay to directly connect the starter motor to the battery and the sliding Pinion gear to turn the starter ring.

Otherwise it really can't draw power off the system.

[mrfixxall]

Start vehicle,remove - treminal on battery. if your guage goes up replace battery(internal short in battery)..if not replace the alternator.

[mikev]

thanks guys going to do a little more troulbeshooting today and get a battery or alternator this afternoon

[Gearhead99]

I'd swap the battery out. How old is the battery??

[mikev]

Ok guys I dont know what i would do without you all I got it fixed. did the diagnostics you guys advised and it was bad alternator. They bench tested it at the store and it failed on all three things diodes regulator and cant rember the other one. So anyhow got the new alternator put it on still wouldnt start so I jumped it off and let it run for about 30 minutes to charge turned it off and click. I ran up to the auto parts store and had them test the battery again and now its a gonner too. I guess the week 1/2 of running it with screwed up alternator and charging it everynight did it in, which sucks cause it looked like a new battery. I am not sure how old it is since I just got the truck in January, so new battery too and now I am good to go. Thanks again for all the advice I was starting to go on a wild goose chase and you guys saved me. thanks again.